COMMENT ON PAPER - TRENDS OF AIRGLOW IMAGER OBSERVATIONS NEAR ADELAIDE, AUSTRALIA BY HECHT,J.H., WALTERSCHEID,R.E., WOITHE,J., CAMPBELL,L.,VINCENT,R.A., AND REID,I.M

The paper by Hecht et al, [1997], hereinafter called HWWCVR, presents results of upper-mesospheric/lower-thermospheric observations performe d from April, 1995 to January, 1996 from Buckland Park Field Station ( 35 degrees S), near Adelaide, Australia. In the abstract, the authors claim to have obtained 'the first seasonal results from the mid-latitu de southern hemisphere mesopause region', regarding (among other param e ters) temperatures. Further, this statement is again repeated in the Conclusions: 'Finally, the work presents the first set of seasonal te mperature variations from the mesopause region in the mid latitude sou thern hemisphere'. The published literature offers much contrary evide nce to this claim, and its inclusion would have placed the contributio n of the HWWCVR work in its proper context as a confirmation of the ea rlier investigations. Papers on southern midlatitude mesopause region seasonal temperature variations have been available in the open litera ture for nearly 30 years, starting with the work of Armstrong [1968] a t Camden, Australia, and more recently, the two-year investigation by Greet and Jacka [1989] at Mount Torrens (also near Adelaide), Australi a. At southern midlatitude locations other than Australia, there has b een the report published by Scheer and Reisin [1990]. This paper conta ins results from 32 degrees S in Argentina, for both the OH(6-2) and t he O-2(0-1) bands (the same airglow bands employed by HWWCVR), and is based on 54 nights of measurements done in four campaigns from 1984 to 1987. Also it reports the typical (warm winter) mesopause variation f or the OH layer, and an unusual, cold-winter, temperature variation at the height of the O-2 emission. In addition, Scheer and Reisin found that OH temperatures were warmer than the O-2 temperatures during wint er. In HWWCVR's Figure 1, which shows nocturnal mean rotational temper atures of OH and O-2, a similar and confirming behavior is evident. Wi th reference to their Figure I, HWWCVR further state that 'These are t he first measurements of mesopause temperatures in the mid-latitude so uthern hemisphere', neglecting all earlier work from the midlatitude r egions of the Southern Hemisphere, such as Argentina [Scheer, 1987, 19 95; Scheer and Reisin, 1990; Reisin and Scheer, 1996] and Australia [A rmstrong, 1968, 1975; Greet and Jacka, 1989; Hobbs et al., 1996]. Repo rts from other latitude regions of the Southern Hemisphere, including Brasil [Takahashi et al., 1974, 1977, 1994] and Antarctica [Hernandez et al., 1992, 1995; Greet et al., 1994; Sivjee and Walterscheid, 1994; Williams, 1996] also exist; however, they may not be directly relevan t to the primary context of HWWCVR. Temperature data from the SME sate llite are also available with complete seasonal coverage between 40 de grees S and 40 degrees N [Clancy and Rusch, 1989], albeit limited in l ocal time coverage. With respect to the observed temperature differenc e between the OH and the O-2 layers, as shown in Figure 1 of HWWCVR (a nd comparison with Figure 1 in Scheer and Reisin [1990]), it should be remembered that systematic errors due to uncertainties in transition probabilities [see, e.g., Turnbull and Lowe, 1989; Scheer et al., 1994 ] as well as instrumental factors [e.g., Hecht et al., 1995] can easil y combine to cause systematic uncertainties of the order of 10K for OH . A similar uncertainty would be expected for O-2 temperatures. In res ponse to Hecht et al.'s reply, we simply emphasize the direct relevanc e of papers in the open literature that predate HWWCVR's confirming re port and which present seasonal results from the midlatitude southern hemisphere mesopause region.